Scanning Tunneling Microscope

The scanning tunneling microscope

Courtesy of UTA NanoFab

Since the first microscope was invented, researchers and scientists around the world have searched for new ways to stretch their understanding of the microscopic world. In 1981, two IBM researchers, Gerd Binnig and Heinrich Rohrer, broke new ground in the science of the very, very small with their invention of the scanning tunneling microscope (STM).

Like no instrument before it, Binnig and Rohrer’s invention enabled scientists to visualize the world all the way down to its molecules and atoms. The STM won the Nobel Prize in Physics in 1986 and is widely regarded as the instrument that opened the door to nanotechnology and a wide range of explorations in fields as diverse as electrochemistry, semiconductor science, and molecular biology.

The STM grew from a collaboration between two scientists who wanted push the boundaries of discovery. Working together at the IBM Zurich Research Laboratory in the late 1970s, Binnig and Rohrer both had backgrounds in superconductivity and were fascinated by the study of atomic surfaces—a topic of extreme complexity and one that perplexed scientists because of the distinct characteristics of the surfaces. But they were limited in their explorations by the state of existing tools. No existing technology allowed scientists to explore directly a surface’s electronic structure and imperfections.

An ordinary microscope, which employs optical lenses, could view objects smaller than the wavelength of light. An electron microscope could view smaller things with greater clarity than an optical microscope, but still could not clearly view individual atoms.

So Binnig and Rohrer decided to build their own instrument – something new that would be capable of seeing and manipulating atoms at the nanoscale level. To do that, they began experimenting with tunneling, a quantum phenomenon in which atoms escape the surface of a solid to form a kind of cloud that hovers above the surface; when another surface approaches, its atomic cloud overlaps and an atomic exchange occurs.

By maneuvering a sharp metal conducting tip over the surface of a sample at an extremely small distance, Binnig and Rohrer found that the amount of electrical current flowing between the tip and the surface could be measured. Variations in this current could provide information about the inner structure and the height-relief of the surface. And from this information, one could build a three-dimensional atomic-scale map of the sample’s surface.

In January 1979, Binnig and Rohrer submitted their first patent disclosure on the STM. Soon after, with the help of fellow researcher Christoph Gerber, they began the design and construction of the microscope itself.

During their first few months of working on the STM, the two inventors had to make a series of adjustments to their original design to accurately produce measurements on such a miniscule scale. These changes lead to reductions in vibrations and noise; more precise control of the scanning tip’s location and movement; and improved sharpness of the probe tip itself.

Their first experiment involved the surface structure of a crystal of gold. The resulting images showed rows of precisely spaced atoms and broad terraces separated by steps one atom in height. “I couldn't stop looking at the images,” Binnig said in his Nobel lecture about those first experiments. “It was entering a new world.”

More refinements to the microscope improved the precision of the mechanical design and resulted in increasingly clearer images. And soon the significance of Binnig and Rohrer’s invention started reaching scientists around the world, who suddenly had access for the first time to the nanoscale world of individual atoms and molecules.

Since the STM could also be used to push and pull individual atoms around, it also marked the first time that humans could manipulate objects that small.

In awarding Binnig and Rohrer the Nobel Prize in Physics just five years after the first STM was built, the Nobel committee said the invention opened up “entirely new fields... for the study of the structure of matter.”

Binnig and Rohrer’s breakthrough invention was the starting point for research in nanotechnology—a field that IBM went on to pioneer. And because of its high resolution imaging power and broad applicability, the STM has found major applications in the fields of physics, chemistry, engineering and materials science.

The atomic force microscope (AFM), an offspring of the STM that was developed by Binnig in 1986, started a new field of microscopy by making it possible to image materials that were not electrically conductive. In addition to the AFM, Binnig and Rohrer’s scanning tunneling microscope gave rise to a whole family of related instruments and techniques that have revolutionizing our ability to view, explore and manipulate surfaces and materials that were not previously observable.